This invention relates to semiconductor devices. More particularly, it is concerned with methods of fabricating semiconductor devices having recessed gate structures.
The static induction transistor is a field effect semiconductor device capable of operation at relatively high frequency and power. These transistors are characterized by a short, high resistivity semiconductor channel region which may be controllably depleted of carriers. The current-voltage characteristics of the static induction transistor are generally similar to those of a vacuum tube triode. These devices are described by Nishizawa et al. in U.S. Pat. No. 3,828,230 issued Aug. 6, 1974, and in U.S. Pat. No. 4,199,771 issued Apr. 22, 1980.
The static induction transistor generally uses vertical geometry with source and drain electrodes placed on opposite sides of a thin, high resistivity layer of one conductivity type. Gate regions of opposite conductivity type are positioned in the high resistivity layer on opposite sides of the source. During operation a reverse bias is applied between the gate region and the remainder of the high resistivity layer causing a depletion region to extend into the channel region below the source. As the magnitude of the reverse bias is varied, the source-drain current and voltage derived from an attached energy source will also vary.
Recessed gate static induction transistors which have improved characteristics are described in United Kingdom Pat. application No. 2,026,237 which was published on Jan. 30, 1980, and in an article "High Performance Microwave Static Induction Transistors" by Cogan et al published in the proceedings of the International Electron Devices Meeting (IEEE) Dec. 5, 6, and 7, 1983, Washington D.C., Paper 9.5, pages 221-224.
In fabricating recessed gate devices the gate regions are formed at the bottoms or end walls of grooves or trenches in the body of silicon material. Metal contacts are applied to the gate regions at the end walls of the grooves in order to make electrical connection thereto. Typically a layer of metal, for example aluminum, is deposited, and then selectively removed to leave metal contacts in the desired pattern. It has been difficult, however, to apply the metal and then remove it so that the metalization at the end walls of the grooves is satisfactory and no metal remains on the side walls of the grooves.